Modern gas turbines often operate at extremely high temperatures. The effect of high temperature on components of the turbine, like an aerofoil, an end wall, a turbine blade and/or stator vane, can be detrimental to the efficient operation of the turbine and can, in extreme circumstances, lead to distortion and possible failure of components or the blade or vane, respectively. In order to overcome this risk, high temperature turbines may include holes in hollow blades or vanes for film cooling purposes.
From U.S. Pat. No. 5,653,110 it is known to provide a substrate, like a blade or a combustor casing of a turbine, with inclined holes which extend through the substrate from a first surface to a second surface ending in a fluid injection point. The holes guide a cooling fluid from the first surface to the second surface, wherein the first surface is cooler than the second hot surface. The second surface has a seamless straight groove to improve the cooling effectiveness of the fluid and thus a film cooling of the hot surface of the substrate.
Problems arise when turbulence occurs at the injection point or downstream of the injection point at the hot surface and the adhesion of the fluid film to the hot surface fails leading to an insufficient cooling of the hot surface of the aerofoil.